Tag: chemistry

Questions Related to chemistry

pH can be detected by :

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. litmus paper

  2. pH meter

  3. phenolphthalein

  4. all of the above

Show answer
Correct Option: D
Explanation:

Indicators may be used to measure pH, by making use of the fact that their color changes with pH. Visual comparison of the color of a test solution with a standard color chart provides a means to measure pH accurate to the nearest whole number. Litmus paper is most widely used to check the pH of a solution. pH meter gives the strength of acidity or basicity of a solution. Phenolphthalein can be used to distinguish between acids and bases.

Unknown metal Appearance Reactions with dilute HCl Reaction with dilute HNO$ _3$
 (1) Dull gray solid with white oxide coating  Dissolved with bubbles of clear gas  Dissolved with bubbles of clear gas
 (2) Solid; lustrous smooth silver-gray surface No reaction  Dissolved with bubbles of orange gas

The addition of dilute HNO$ _3$ to unknown metal (2) produced an orange gas. Which of the following is the orange gas?

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. Cl$ _2$

  2. H$ _2$

  3. O$ _2$

  4. CO$ _2$

  5. NO$ _2$

Show answer
Correct Option: E
Explanation:

The addition of dilute $HNO _3$ to unknown metal (2) (silver metal) produced an orange gas nitrogen dioxide $\displaystyle (NO _2)$.
Note: Various gases have following colours.
$Cl _2-$ green
$H _2-$ colorless
$O _2-$ colorless
$CO _2-$ colorless
$NO _2-$ orange/brown

Which of the following would seperate $\displaystyle { H } _{ 2 }{ S }$ at pH < 7 ?

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. $\displaystyle { Zn }^{ 2+ },{ Co }^{ 2+ }$

  2. $\displaystyle { Cu }^{ 2+ },{ Cd }^{ 2+ }$

  3. $\displaystyle { Cu }^{ 2+ },{ Cr }^{ 3+ }$

  4. $\displaystyle { Cu }^{ 2+ },{ As }^{ 3+ }$

Show answer
Correct Option: C
Explanation:

$\displaystyle { H } _{ 2 }{ S }$ would separate $\displaystyle { Cu }^{ 2+ },{ Cr }^{ 3+ }$ at pH<7 .
$Cu^{2+} +  H _2S \uparrow \rightarrow  \underset {black  ppt} {CuS} + 2H^+$

pH stands for :

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. power of hydrogen

  2. power of hydroxide

  3. purity of hydrogen

  4. purity of hydroxide

Show answer
Correct Option: A
Explanation:

pH is the negative log of hydrogen ion concentration in a water-based solution. The term 'pH' was first described by Danish biochemist Soren Peter Lauritz Sorensen in 1909. pH is an abbreviation for 'power of hydrogen' where 'p' is short for the German word for power and 'H' is the element symbol for hydrogen.

Which of the following liquids can be used to check pH?

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. Phenolphthalein

  2. Bromothymol blue

  3. Both $A$ and $B$

  4. None of the above

Show answer
Correct Option: C
Explanation:

A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually. Hence, a pH indicator is a chemical detector for hydronium ions ($H _3O^+$) or hydrogen ions ($H^+$). Bromophenol blue is used as a pH indicator, a color marker, and a dye. As an acid-base indicator, its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to blue at pH 4.6; this reaction is reversible. Phenolphthalein is often used as an indicator in acid-base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.

State True or False.
The strength of acidity or basicity is not given by $pH$ paper.

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

$pH$ paper is the litmus paper which helps in identification of whether the solution is acidic or basic in nature. It does not help to determine the strength of acidity or basicity of a solution.

Acidic compounds has a pH :

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. equal to $14$

  2. less than $7$

  3. equal to $1$

  4. greater than $0$

Show answer
Correct Option: B
Explanation:

The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.


$\begin{matrix}&pH=X\Cr _2O _7^{2-}&\rightleftharpoons&CrO _4^{2-}\(orange)&pH=Y&(green)\end{matrix}$
This change is based on change in $pH$. Probable values of $X$ and $Y$ cannot be :

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. 8, 6

  2. 8, 10

  3. 4, 6

  4. change is independent of $pH$

Show answer
Correct Option: B,C
Explanation:

$\begin{matrix}&pH=X= 8  \ or \ 4 \ (less\  than \ Y) \Cr _2O _7^{2-}&\rightleftharpoons&CrO _4^{2-}\orange&pH=Y= 10\  or \ 6  \ (more\  than\  X) &green\end{matrix}$

As dichromate ion changes to chromate in acidic medium( less pH) , whereas chromate changes to dichromate in basic medium ( higher pH)
                             Lower pH (acidic medium) $\rightarrow$
$ Cr _2O _7^{2-}<========================>CrO _4^{2-}$
                            $\leftarrow$ Higher pH ( basic medium)

Unknown metal Appearance Reactions with dilute HCl Reaction with dilute HNO$ _3$
  (1) Dull gray solid with white oxide coating  Dissolved with bubbles of clear gas  Dissolved with bubbles of clear gas
  (2) Solid, lustrous smooth silver-gray surface No reaction  Dissolved with bubbles of orange gas

Which of the following represents unknown metal (1)  ?

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. Mercury

  2. Copper

  3. Zinc

  4. Iron

  5. Silver

Show answer
Correct Option: C
Explanation:

Unknown metal (1) could be zinc as it is dull gray solid with white oxide coating.
Note: Mercury is a liquid, copper is brownish, iron has orange brown coating of oxide (rust) and silver has gray-black colour.

$\displaystyle \underset {orange}{Cr _2O _7^{2-}}\,\overset {pH=x}{ \underset {pH = y}{\leftrightarrows}}\, \underset {green}{CrO _4^{2-}}$. 


This change is based on change in pH. 

Find values of x and y  :

hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

  1. $8, 6$

  2. $8, 10$

  3. $4, 6$

  4. change is independent of pH

Show answer
Correct Option: A
Explanation:

The process involves the equilibrium between chromate (VI), dichromate (VI) and hydrogen ions:


$2{ Cr{ O } _{ 4 }^{ 2- } } _{ \left( aq. \right)  \left( yellow \right)  }+2{ { H }^{ + } } _{ \left( aq. \right)  }\rightleftharpoons { { Cr } _{ 2 }{ O } _{ 7 }^{ 2- } } _{ \left( aq. \right)  \left( orange \right)  }+{ { H } _{ 2 }O } _{ \left( l \right)  }$

The addition of acid encourages the equilibrium towards the right (pH=6), producing more orange colored dichromate (VI) ions. The addition of hydroxide ions causes the concentration of hydrogen ions to decrease, and this brings the equilibrium back to the left-hand side, regenerating yellow chromate (VI) ions.